1. Technical Field
The present invention relates to an image forming apparatus, and in particular relates to toner pattern density correction of a toner pattern formed on a secondary transfer belt in the image forming apparatus.
2. Background Art
In an image forming apparatus employing electrophotography, to maintain optimum image density of the printed image it is necessary to execute an image density control operation periodically.
The image density control operation includes a first density control and a second density control. The first density control is performed out of synchrony with a printing operation. The second density control is performed in synchrony with the printing operation during printing using a blank area between transfer sheets or at an end of the sheet. Herein, the term “image forming apparatus” means and includes a copier, a printer, a facsimile machine, or a multifunction apparatus combining the capabilities of these apparatuses, and can also include any device that forms an image.
In the first density control, a plurality of monochrome toner patterns is formed on an intermediate transfer belt, and density of each toner pattern is detected by a reflection-type optical sensor. Based on a relation between the detected amount of adhered toner and image forming conditions such as charging bias, development bias, and exposure, the image forming condition in printing is determined.
To perform the first density control, however, the printing operation needs to be suspended. As a result, productivity in continuous printing will be reduced. Therefore, the first density control is performed only when the image fluctuation is high, thereby preventing the productivity from decreasing. For example, the first density control is performed when the power is on, before the start of printing, after a predetermined number of prints are generated, or when image forming operation is terminated.
In the second density control, a plurality of toner patterns for adjusting image density of each color is formed outside the image area during continuous printing, and density of each toner pattern is detected by a reflection-type optical sensor. A target adhesion amount stored in a memory and the detected amount of adhered toner are compared and, based on the detection result, toner density of the developer in the developing device is adjusted. With this, the image density between the two density controlling operations is maintained.